P8: The striving by which each thing strives to persevere in its being involves no finite time, but an indefinite time.

Dem.: For if {the striving by which a thing strives to persevere in its being} involved a limited time, which determined the thing’s duration, then it would follow just from that very power by which the thing exists that it could not exist after that limited time, but that it would have to be destroyed. But (by P4) this is absurd. Therefore, the striving by which a thing exists involves no definite time. On the contrary, since (by P4) it will always continue to exist by the same power by which it now exists, unless it is destroyed by an external cause, this striving involves indefinite time, q.e.d.